Elastic constants, interatomic forces, and equation of state of β-oxygen at high pressure

The six independent elastic constants of β-oxygen have been measured over a pressure range extending from 6.0 to 9.5 GPa. Neither central forces between individual atoms, nor central forces augmented by the interactions between axial distributions of charge can give a reasonable account of the data. Force constant matrices were found which can account for the elastic data and the previously observed librational frequency. These matrices are based on general, short range forces with many-body interactions only among atoms contained in the same pair of molecules. Vibrational densities of states, distributions of individual-mode Grüneisen parameters, heat capacities, and the equation of state derived from the pressure dependence of the elastic moduli are presented.